The increasing concern for safety has resulted in increased efforts towards providing safer materials for commercial and household use. One particular area of need is that of providing flame retardant plastic products, many of which are now required to meet certain flame retardant criteria established by local and federal governments as well as by the manufacturers of such products. One particular set of conditions commonly accepted and used as a standard for flame retardancy is that which is set forth in Underwriter's Laboratories, Inc. Bulletin 94 which proscribes certain conditions by which material are rated for self-extinguishing characteristics.
It is known that various halogen-containing, flame retardant additives can be employed to render plastic products self-extinguishing or flame retardant. Such flame retardant additives are typically employed in amounts sufficient to be effective for their intended purpose; generally, on the order of about 5-20% by weight based upon the weight of the plastic composition. In many instances, use of these flame retardants in such amounts can have a degrading affect upon the plastic compositions to be rendered flame retardant often resulting in the deterioration of valuable physical properties of the base polymer. This is particularly so when known flame retardant additives are employed with polycarbonate resins since many of these additives have a degrading affect upon the base polymer typically resulting in the discoloration and a loss of impact strength.
It is also known that blends and/or copolymers of halogen-containing copolycarbonates and aromatic thiodiphenols can be employed to obtain flame retardant compositions. For example, U.S. Pat. No. 4,043,980 discloses polycarbonate compositions obtained as the reaction product of an aromatic diol, a halogenated phenol, an a carbonic acid coreacted with an aromatic thiodiphenol (TDP), which compositions exhibit flame retardancy stated to be the result of the synergism between the sulfur and the halogen present in the compositions. It is also disclosed that such compositions overcome the detrimental critical thickness effect, i.e., that thickness at which notched Izod values of a test sample begin to decrease, due to the presence of sulfur in the composition.
In U.S. Pat. No. 4,174,359, flame retardant polycarbonate compositions are disclosed which are obtained as blends of an aromatic diphenol-TDP copolymer and a halogen containing compound. The compositions can also contain small amounts of a sulfonic or carboxylic acid salt, which salt is preferably perfluorinated. However, both of these patents teach that the presence of the halogen containing moiety is essential in the compositions disclosed.
Other sulfur-containing polycarbonate compositions are also known such as crystalline copolycarbonates obtained as the reaction of polycarbonate and TDP as disclosed in "Polycarbonates and Mixed Polycarbonates bases on Bis(4-hydroxyphenyl)sulfide", O. V. Smirnova, G. S. Kolesnikov, A. K. Mikitaeo and T. G. Krichevskaya (Mosk. Khim-Teckhnol. Inst. im Mendeleeva, Moscow), Vysokomol Soldin, Ser. 4 10(1), 96 101(1968) (Russ), also reported in "Chem. Abstracts"; 68, 1968.
In addition, U.S. Pat. No. 3,398,212 discloses copolymers and blends of copolycarbonates and copolyesters prepared from halogenated or non-halogenated polycyclic gem-bisphenols and TDP.
Further, in an article entitled "Linear Aromatic Polyesters of Carbonic Acid", H. Schnell (Ind. Chem. Eng., 1959) there is disclosed crystallizable polycarbonates which contain TDP.
There is a need, however, for generally amorphous, non-crystalline polycarbonates which exhibit flame retardancy and improved thick section impact. It is, therefore, an object of the instant invention to provide such polycarbonate compositions.